Patients achieving negative surgical margins after complete resection of tumor receive postoperative chemotherapy comprising leucovorin calcium IV over 2 hours and fluorouracil IV continuously over 46 hours on days 1 and 15 OR oxaliplatin IV over 2 hours, leucovorin calcium IV over 2 hours and fluorouracil IV continuously over 46 hours on days 1 and 15. Treatment repeats every 28 days for up to 4 courses in the absence of disease progression or unacceptable toxicity.